This invention is directed to sedimentation apparatus and in particular to corner sweep rake mechanisms for clarifiers or thickeners of the type utilizing non-circular or cornered settling tanks.
Settling tanks of the type mentioned are of a generally square-shaped configuration in horizontal cross-section and are well known for use in the treatment of wastewater or sewage in the separation of solids from a solids-liquid suspension. These settling tanks generally comprise vertical sidewalls with an overflow launder provided about the upper periphery of the sidewalls for receiving the supernatant liquid from the solids-liquid suspension. A central rotary rake structure is provided for raking sludge or other solids that settle from the liquid suspension to a central sump outlet located in the tank bottom. The main raking structure usually consists of a pair of 180.degree. displaced radially extending rake arms which are rotatably mounted at the base of a center support column within the tank. Since the raking area or sweep of the raking structure is limited by the diameter of the path or rotation of the rake arms, it is necessary and well known to provide auxiliary or corner sweep mechanisms attached or hinged to the outer ends of the main rake structure which are extendible into the corners of the tank bottom to sweep solids settled therein which are not reachable by the rake arms.
The mentioned square type settling tank has met with success, for example, in installations where a circular tank is not desirable due to limited space availability. The corner sweep mechanisms for these known settling tanks comprise a supplemental rake or sweep arm structure pivotally mounted to the main rake arm and urged into contact with the inner wall surfaces of the settling tank by counterweights or by the combination of tension springs and counterweights. As the rake structure is rotated past the cener line of the tank the sweep arm is maintained in a retracted position and as the rake arm passes a corner the sweep arm is extended into and around the corner curve of the tank to clear the tank bottom in these areas of settled solids by raking the latter into the path of the rake blades of the main rake structure.
Prior art corner sweep raking mechanisms are typified by the devices disclosed in the following U.S. Pat. Nos.:
1,457,794 PA1 1,603,995 PA1 1,957,185 PA1 2,053,636 PA1 2,238,024 PA1 2,259,230 PA1 2,261,487 PA1 2,863,564 PA1 3,770,132
Although the corner sweep mechanisms of these prior disclosures may have proven effective for their intended purposes they generally comprise excessive structural mechanisms which include sheaves, cables, counterweights and yoke structures or require special castings or the like. As a result known arrangements are of a generally heavy or complex construction which increases the torque and force requirements of the main rake and drive structure during operation.
It is an object of the present invention to provide a novel corner sweep mechanism for a non-circular settling tank without the utilization of counterweights.
Another object is to provide a novel corner sweep mechanism which is of a lightweight and buoyant construction.
A further object is to provide a corner sweep mechanism having integral means for readily adjusting the height of the sweep arm relative to the tank bottom.